1. Field of the Invention
The present invention relates generally to telecommunications systems and methods for managing ported calls, and specifically to Service Switching Points (SSPs) selectively performing Local Number Portability (LNP) queries for calls routed to Interexchange Carriers (IXC).
2. Background and Objects of the Invention
Since the beginning of the telephone in the 1870's, signaling has been an integral part of telephone communications. The first telephone devices depended on the receiving party standing next to the receiver at the time of the call. Later, after the formation of the Bell Telephone Company, Alexander Graham Bell's assistant Watson invented the telephone ringer, eliminating the foreknowledge requirement. By lifting the receiver and allowing DC current to flow through the phone and back through the return of the circuit, a lamp would be lit on the exchange operator's switchboard to signal the operator that a call was trying to be placed.
However, early signaling methods were somewhat limited because they used the same circuit for both signaling and voice. In addition, they were analog and had a limited number of states, or values, that could be represented. In the early 1960's, Europe began digitizing the network, removing the signaling from the voice network, and placing the phone signals on a separate network. With this division of signaling and voice, the call setup and tear-down procedures required with every phone call were performed faster, while reserving the separate voice and data circuits for use when a connection was possible, e.g., no voice connection is needed when the called party's number is busy. Common Channel Signaling (CCS), which uses a digital facility, but places the signaling information in a time slot or channel separate from that of the voice or data it is related to, has become the foundation for telecommunications today.
In modern telecommunications networks, signaling constitutes the distinct control infrastructure that enables provision of all other services. It can be defined as the system that enables stored program control exchanges, network databases, and other "intelligent" nodes of the network to exchange: (a) messages related to call setup, supervision, and tear-down; (b) information needed for distributed applications processing (inter-process query/response); and (c) network management information.
In addition, the Intelligent Network (IN) and the new Advanced Intelligent Network (AIN) have made possible the transfer of all types of information through the telephone network without special circuits or long installation cycles. In the IN/AIN, everything is controlled or configured by workstations with user-friendly software. Telephone service representatives can, therefore, create new services and tailor a subscribers service from a terminal while talking with the customer. These changes are immediately and inexpensively implemented in the switches, rather than by the more traditional method: expensive programming changes made by certified technicians.
The IN consists of a series of intelligent nodes, each capable of processing at various levels, and each capable of communicating with one another over data links. The basic infrastructure needed is composed of various signaling points, which both perform message discrimination (read the address and determine if the message is for that node), and route messages to other signaling points. The basic three types of signaling points are: (1) Service Switching Points (SSPs); (2) Signal Transfer Points (STPs); and (3) Service Control Points (SCPs), each of which are described in more detail hereinafter.
With reference now to FIG. 1 of the drawings, the many Service Switching Points (SSPs) 100 serve as the exchanges in a telephone network 90, a portion of which is shown in FIG. 1. Across the country, groups of SSPs 100 are divided into separate Local Access Transport Areas (LATA) 130. Calls placed within a single LATA 130 are handled by the local exchange carriers (LEC), e.g., GTE, while calls placed interLATA, that is between separate LATAs 130, are handled by Interexchange Carriers (IXC), e.g., AT&T, which provide long-distance service to customers within a number of LATAs. The LECs and IXCs are separate types of SSPs 100, which provide either local or long-distance service respectively to subscribers.
The STP 110 serves as a router, and switches messages received from a particular SSP 100 through the network 90 to their appropriate destinations (another SSP 100). As is also understood in the art, the STP 110 receives messages in packet form from the SSPs 100. These packets are either related to call connections or database queries. If the packet is a request to connect a call, the message must be forwarded to a destination end office (another SSP 100), where the call will be terminated.
If, however, the message is a database query seeking additional information, the destination will be a database. Database access is provided through the Service Control Point (SCP) 120, which does not store the information, but acts as an interface to a computer that houses the requested information.
Presently, a subscriber on one SSP 100 has the ability to move to a different SSP 100 within the same LATA 130 while retaining their public directory number. This is referred to as local number portability. One key advantage of local number portability is that other subscribers can connect to the ported subscriber without any changes to their dialing procedures.
If a subscriber has been ported-out to another SSP 100, the Initial Address Message (IAM) sent by the originating SSP 100 must be modified to account for the change in the terminating SSP, as is understood in the art. The Local Number Portability (LNP) database is the database that holds the Location Routing Numbers (LRN), which are ten-digit numbers used to uniquely identify the switch that has the ported-out number. Specifically, the LRN is the number for the recipient switch, which is the switch that has ported-in a number from another switch (called a donor switch). This ported-in number was not previously served by the recipient switch.
Typically, the SSP 100 sends a LNP query to the SCP 120, which accesses the LNP database in order to retrieve the routing information for a ported subscriber. The query response by the SCP 120 provides that SSP 100 with the pertinent LRN, which is populated (that is placed) in the Called Party Number (CPN) parameter in the IAM. The Ported Dialed Number (PDN), e.g., the actual dialed digits for the ported-out subscriber, is placed in the Generic Address Parameter (GAP) in the IAM. The Forward Call Indicator (FCI) M-bit in the IAM is then updated to indicate that the number has been translated. The FCI M-bit is used as a fail-safe mechanism to prevent more than one LNP query from being launched on a call.
If the end-user has not been ported-out, the SCP 120 will return the actual dialed number, not the LRN, to be stored in the CPN parameter. In this case, the GAP is not included in the IAM. It should be noted that the FCI M-bit is always set to "Number Translated" after any LNP query, regardless of whether the end-user has been ported-out or not.
Each subscriber has associated therewith a three-digit Numbering Plan Area (NPA), e.g., area code, and a three-digit Office Code (NXX), e.g., the first three digits of a seven-digit telephone number. Each SSP stores within it a list of LNP triggers, which are the NPANXX digit streams associated with subscribers who have the ability to port, whether or not any subscribers having that NPANXX actually are ported. Every time a call is placed to a subscriber on a different SSP than the calling party's SSP, the originating SSP, which is the SSP responsible for the subscriber placing the call, checks the LNP trigger for the called party to determine if a LNP query should be performed prior to routing the call to the called party's switch. Each LNP trigger has a condition known as a LNP trigger criteria type associated with it. The LNP trigger criteria types are indicators stored in the switch by command or other method, which can be set to either "query" or "do not query", depending upon different conditions.
Presently, for calls to subscribers having a NPANXX which is a LNP trigger, which are routed to an Interexchange Carrier (IXC), e.g., long-distance calls, such as 1 plus dialing, 10XXX dialing (such as 10288 for AT&T), or 101XXXX dialing, the LNP trigger criteria type is always set to either "query", which instructs the originating SSP to perform a LNP query to the SCP before routing the call to the IXC, or "do not query", which instructs the originating SSP to never perform a LNP query prior to routing the call to the IXC, regardless of the LNP querying capability of the IXC. Therefore, for conventional systems to be implemented successfully, all carriers (IXCs) would need to possess LNP querying capability to deliver calls to ported numbers. Otherwise, the calls would be routed to the donor switches, which results in excessive switching and delays. However, with the increase in the number of small sized competitive access providers (CAPs) entering the long-distance carrier market, it will not be possible for all the small carrier companies to provide LNP querying capability.
Existing systems also present a problem in the case where a single switch acts as both an end office (EO) and an IXC without loop back of calls, which is explained hereinafter. Many EO/IXC switches have a logical boundary between the EO services and the IXC services. Therefore, when a long-distance call is placed, the EO actually routes the call on trunk lines out of the switch back to the IXC in the switch, which enables the EO and the IXC to function independently within the same switch. Thus, for a call to a NPANXX having a "do not query" LNP trigger criteria type associated with it, the EO will route the call to the appropriate IXC, either within its switch or to another chosen by the subscriber, for a LNP query.
However, when no logical boundary exists between the EO and the IXC, and the internal IXC is used to place a call to a NPANXX having a "do not query" LNP trigger criteria type associated with it, the EO/IXC does not perform the LNP query. Instead, the EO/IXC routes the call to the donor switch, thus incurring a charge from the donor switch for a LNP query which the EO/IXC was capable of performing.
Furthermore, conventional systems employing LNP querying for IXC routed calls do not allow local service providers (SSPs) to sell their LNP querying capability on a per carrier basis, which is inefficient for both the SSPs and the IXCs.
It is therefore one object of the invention to provide LNP querying by the SSP for calls routed to selective Interexchange Carriers that do not possess LNP querying capability to prevent routing of calls to donor switches.
It is a further object of the invention to allow local SSPs to sell their LNP querying capability on a per carrier basis.
It is still a further object of the invention to allow the EO within the EO/IXC single switch, which does not have the loop back of calls ability, to perform a LNP query for the IXC regardless of whether the LNP trigger criteria type is set to "query" or "do not query".